Improvement of Cerium on Photosynthesis of Maize Seedlings Under a Combination of Potassium Deficiency and Salt Stress

Added Ce3+ can partly substitute for Ca2+ or Mg2+ and improve photosynthesis under the deficiency of these elements, but very few studies focused on photosynthetic improvement in maize seedlings caused by K+ deficiency, salt stress, especially a combination of K+ deficiency and salt stress. In the present study, the effects of Ce3+ on the photosynthesis of maize seedlings under the three different stresses were investigated. The results showed that added Ce3+ under various stresses increased the ratios of free water/bound water and of K+/Na+, the pigment contents, the values of Fv/Fm, Y(II), ETR(II), Y(NPQ), Qp, qL, NPQ, and qN of photosystem II (PSII), the values of Y(I) and ETR(I) of photosystem I (PSI) and the expression levels of LhcII cab1 and rbcL, and decreased the values of Y(NO) and Y(NA). This implied that added Ce3+ depressed ion toxicity, photodamage of PSII, and acceptor side constraints of PSI, and enhanced adjustable energy dissipation, the responses of photochemistry, and carbon assimilation caused by K+ deficiency, salt stress, and the combination of K+ deficiency and salt stress. However, Ce3+ mitigation of photosynthetic inhibition in maize seedlings caused by the combined stresses was greater than that of salt stress, and Ce3+ mitigation under salt stress was greater than that under K+ deficiency. In addition, the results also showed that Ce3+ cannot improve photosynthesis and growth of maize seedlings under K+ deficiency by substituting for K+.